In two-wheeled motor vehicles, namely, in motorcycles, a fuel injection system using an injector to inject fuel has come to be widely used in place of carburetor. In such fuel injection systems, fuel pressurized by means of a plunger-type high-pressure fuel pump device is supplied to the injector attached to the engine.
Since the plunger-type high-pressure fuel pump device is configured to increase the pressure of fuel for delivery by moving the plunger, however, it cannot be expected to perform the function of sucking up fuel stored in the fuel tank. Thus, in motorcycles, the plunger-type high-pressure fuel pump device is located at a lower level than the fuel tank so as to utilize the weight of fuel to suck in the fuel, or is arranged within the fuel tank to directly suck in the fuel stored in the fuel tank.
In motorcycles in particular, many devices such as the fuel tank, engine and transmission are densely arranged in a limited space surrounded by the front wheel, the fuel tank, the rear wheel and the seat, and therefore, the high-pressure fuel pump device, which is single in number and thus is easier to secure a space for fitting, is used to supply fuel stored in the fuel tank to the injector.
With the recent diversification of motorcycles, the high-pressure fuel pump device also is required to cope with such diversification and sometimes needs to be mounted at a location near the fuel tank or the engine where the high-pressure pipe can be shortened in length.
However, the high-pressure fuel pump device cannot be expected to perform the function of sucking up fuel stored in the fuel tank as stated above, and thus it is often the case that the high-pressure fuel pump device cannot be mounted on motorcycles.
In four-wheeled motor vehicles (automobiles), a feed pump device is provided separately from the high-pressure fuel pump device to suck up fuel stored in the fuel tank, and the fuel is supplied from the feed pump device to the high-pressure fuel pump device, as disclosed in Patent Document 1. In such four-wheeled motor vehicles, to avoid heat damage, the feed pump device is usually arranged within the fuel tank to be cooled by the fuel in the fuel tank, and the fuel is supplied to the high-pressure fuel pump device while suppressing vaporization of the fuel. This configuration could be applied to motorcycles as well.